It is known in the art to inject sand containing a radioactive carrier into fractured earth formations in oil or gas wells to determine the location of such fractures. As an example, reference is made to Mihram, et. al., U.S. Pat. No. 2,951,535. Conventionally, a sand/fluid mixture is injected into a fractured oil well after it has been pressurized by, e.g., a slurry pump. Feeding the slurry pump is a line from a blender, which blends a fluid with sand, commonly termed a proppant. Radioactive sand is conventionally injected by an injection tool in the line between the blender and the slurry pump. The passage of the proppant as mixed with the radioactive additive through the slurry pump causes possible radioactive contamination of the slurry pump and all down-line apparatus, and is thus undesirable. However, conventionally, the injection tool has not been able to be placed on the pressurized side of the slurry pump, as the presence of pressure on the radioactive proppant injecting mechanism causes the sand to clog, especially when there is a change of pressure in the pressurized proppant line. Thus, the location of the injection tool has heretofore been restricted to a low pressure point on the sand proppant slurry line before the pump.
Pressure equalizing conduits are known in the fields of applying dry chemicals to oil wells and more generally for adding a dry material to a liquid. Examples of such tubes can be found in Kierbow, et al., U.S. Pat. Nos. 4,265,266 and Brewer, 3,160,210.
However, these prior art pressure equalizing tubes are not designed for use in high-pressure applications, as evidenced by the disposition of the equalizing tube in each case in a position exterior to the dry material injector housing. Rather than equalizing two chambers at relatively high pressures, Kierbow discloses the venting of pressure on the forward side of a horizontal screw conveyor to ambient atmospheric pressure. Brewer discloses a tube exteriorally connecting a region of a cylinder behind a piston pressing a dry chemical agent downward into a horizontal screw conveyor to a point situated midway along the screw conveyor. In addition to being of relatively complex construction, this positioning of a pressure equalization tube would still not prevent clogging in the remaining distance of the screw conveyor. Both Kierbow and Brewer also disclose pressure equalization tubes as used in connection with horizontal screw conveyors, rather than a pressure equalization tube used in connection with a dispenser operating using the force of gravity to move the additive. A need has thus arisen for a radioactive proppant dispenser which may be connected to the high pressure side of a fracturing system in order to accurately and automatically meter desired amounts of radioactive proppant without clogging.